This application claims priority to Japanese Patent Application No. 2001-251912, filed on Aug. 22, 2001, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
The present invention relates to outboard motors for watercraft, and in particular, a lubricant pump seal for outboard motors.
2. Description of the Related Art
Outboard motors containing internal combustion engines are commonly used for powering watercraft. A housing, which is mounted to a transom of the watercraft, typically encloses the engine. Rotation of an output shaft of the internal combustion engine drives a driveshaft. The driveshaft drives a water propulsion device, such as a propeller. When the watercraft operates, the propeller is submerged beneath a water surface. Rotation of the propeller moves the watercraft across the water surface.
Internal combustion engines require lubricant for normal operation. Four-cycle engine typically employ a recirculating type of lubrication system. In such a system, a lubricant pump supplies lubricant to a crank chamber and other moving components of the engine. The lubricant pump also circulates lubricant between the crank chamber and a lubricant pan. The lubricant pump is usually located near the coupling of the output shaft and the driveshaft, so that the rotation of the output shaft can be used to drive the lubricant pump.
The lubricant pump typically comprises a pump casing defining a pump chamber. The drive shaft penetrates the pump chamber. A first sealing body seals an upper clearance formed between an upper part of the pump casing and the drive shaft. Second and third sealing bodies seal a lower clearance formed between a lower part of the pump casing and the drive shaft.
The outboard motor interfaces with the body of water upon which the watercraft moves. Lubricant exiting the motor pollutes the body of water. Ideally the outboard motor operates as cleanly as possible in order to protect our limited natural resources. The first and second sealing bodies typically prevent lubricant from exiting the pump casing.
Often, the motor draws in water from the surrounding body of water for cooling the engine and an exhaust system. However, water penetrating the coupling of the output shaft and driveshaft adversely affects the performance and longevity of the engine. Impurities in the water, especially salt, deposit on the shafts and cause corrosion. The corrosion causes the shafts to stick together. The third sealing body is designed to prevent water from entering the pump casing.
However, during operation, the lubricant pump creates negative pressure in the region of the coupling. This negative pressure draws in ambient air and water. The water and moisture contained in the air causes corrosion. Prior attempts at preventing moisture penetration due to negative pressure in the pump chamber have been unsuccessful.
The preferred embodiments of the present lubricant pump seal for an outboard motor have several features, no single one of which is solely responsible for their desirable attributes. Without limiting the scope of this lubricant pump seal for outboard motor as expressed by the claims that follow, certain features are described below. After considering this discussion, and particularly after reading the section entitled xe2x80x9cDetailed Description of the Preferred Embodiments,xe2x80x9d one will understand how the features of the preferred embodiments provide advantages, which include reliable prevention of water penetration into an interior of the lubricant pump.
One aspect of the present invention includes the realization that negative pressure developed by lubricant pump can be relieved, thereby preventing the lubricant pump from drawing humid air or water into the lubricant pump. One preferable way of relieving the pressure is to provide a passage extending from the lubricant pump to a source of dry air. By constructing in the lubricant pump as such, water infiltration into the lubricant pump can be prevented.
In accordance with one preferred embodiment of the present invention, a lubricant pump seal is provided for an outboard motor. The outboard motor comprises a an internal combustion engine, a water propulsion device, a drive shaft configured to transmit torque from the engine to the water propulsion device, and a lubricant pump configured to supply lubricant to the internal combustion engine. The lubricant pump includes a pump casing enclosing a pump chamber. The drive shaft extends through the pump casing. A rotor is housed in the pump chamber for rotation with the drive shaft. A first sealing body for sealing an upper clearance is formed between an upper part of the pump casing and the drive shaft. Second and third sealing bodies for sealing a lower clearance are formed between a lower part of the pump casing and the drive shaft. A fourth sealing body is disposed between the second and third sealing bodies in an axial direction of the drive shaft. The fourth sealing body seals the lower clearance.
The lubricant pump seal preferably further comprises a fluid communication passage between a space in the lower clearance sandwiched between the second and third sealing bodies and a lubricating oil reservoir inside the internal combustion engine. At least a portion of the passage may comprise a groove in an auxiliary pump casing. Alternatively, at least a portion of the passage may comprise a groove in a lower surface of a casing body.
The lubricating oil reservoir may comprise a crank chamber of the engine. Alternatively, the lubricating oil reservoir may comprise a lubricant pan located below a crank chamber of the engine.
The lubricant pump seal preferably further comprises a fluid communication passage between a space in the lower clearance sandwiched between the second and third sealing bodies and an inside space of the cowling. At least a portion of the passage may comprise a groove in an auxiliary pump casing. Alternatively, at least a portion of the passage may comprise a groove in a lower surface of a casing body.
Another aspect of the present invention includes a method of preventing moisture penetration into an interior of a lubricant pump of an outboard motor. The method comprises providing a fluid communication passage between the interior of the lubricant pump and a lubricant reservoir, generating negative pressure within the interior of the lubricant pump, and channeling fluid from the lubricant reservoir to the interior of the lubricant pump, thereby eliminating the negative pressure.
Yet another aspect of the present invention is directed to a method of preventing moisture penetration into an interior of a lubricant pump of an outboard motor. The method comprises the steps of providing a fluid communication passage between the interior of the lubricant pump and a space inside a cowling, generating negative pressure within the interior of the lubricant pump, and channeling fluid from the space inside the cowling to the interior of the lubricant pump, thereby eliminating the negative pressure.
In accordance with a further aspect of the present invention, an outboard motor comprises an internal combustion engine, a propulsion unit driven by the engine, and a housing enclosing the engine and at least a portion of the propulsion unit. A drive shaft extends between the engine and the propulsion unit. A lubricant pump unit is configured to deliver lubricant to the engine. The drive shaft extends through the lubricant pump unit. A seal is disposed between the lubricant pump unit and the drive shaft. Additionally, the outboard motor includes means for relieving a negative pressure generated in the vicinity of the seal.
In accordance with yet another aspect of the present invention, an outboard motor comprises an internal combustion engine, a propulsion unit driven by the engine, and a housing enclosing the engine and at least a portion of the propulsion unit. A drive shaft extends between the engine and the propulsion unit. A lubricant pump unit is configured to deliver lubricant to the engine. The drive shaft extends through the lubricant pump unit. A clearance is defined between the drive shaft and the lubricant pump unit. At least one seal is in contact with the drive shaft and is configured to seal the interior of the lubricant pump unit from an exterior of the pump unit. A passage extends from the clearance to exterior of the lubricant pump unit.